A wide range of mixtures are known in the art from which various types of foam products may be produced. Foams may be produced by providing a thermoplastic material above its melting point with a blowing agent to form a mixture, and subjecting the mixture to a reduction in pressure and simultaneous cooling. Typical thermoplastic materials may be selected from polyolefins, for example, polyethylene. To molten polyethylene may be added a blowing agent known in the art such as pentane, to form a mixture, the whole being done under a pressure greater than atmospheric. When such a mixture is passed from a pressure greater than atmospheric to atmospheric pressure through, for example, an extruder die, the pentane is caused to vaporize while the molten polyethylene simultaneously cools to its solidification point. If the expansion is carried out under sufficient control and conditions known to those skilled in the polymeric foam art, a foam product having cells of pentane contained within a matrix of polyethylene, i.e., polyethylene foam, may be formed.
Other foams may be similarly produced, with but one example being polyurethane foam. Polyurethanes are produced by the reaction of an organic polyol with an organic isocyanate, preferably in the presence of one or more catalysts which promote the reaction between the polyol and isocyanate and reactions between isocyanates and urethanes to produce crosslinked or thermoset foams, as such are generally known to those skilled in the polymer foam art. Production of polyurethane foam is generally carried out by the cocomminutation of the polyol, isocyanate, and blowing agent followed by its immediate and controlled expansion, for once cured, thermoset polyurethane cannot be reprocessed as thermoplastic polyolefin-derived foams can. Typical isocyanates used for polyurethane and polyisocyanurate foam production include without limitation: 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 2,2′-diphenylmethane diisocyanate, toluene diisocyanate, or a functionally-equivalent (with respect to reactivity towards polyols) polymerized form of any of the foregoing as such polymerized forms are known to those skilled in the art. Typical polyols used for polyurethane and polyisocyanurate foam production include without limitation polyester polyols and polyether polyols, as such are known to those skilled in the art.
Various catalysts have been developed and discovered which are useful for promoting the reaction between the polyol and isocyanate portions from which polyurethanes are derived. Typically, metal cations displaying monovalency are useful in this regard, such as the alkali metals including sodium, potassium, rubidium, and cesium, with potassium being especially preferred. However, since most potassium salts are very soluble in water but are not normally soluble in organic matrices owing to the general lack of polarity and hydrophillicity of organic matrices in general, and particularly the organic components from which polyurethanes are formed (polyol and isocyanate), those desiring to employ cations such as potassium and particular anions have generally been limited in the prior art with respect to the anions which accompany the potassium, with polycyclic aromatic anions such as naphthenates and higher carboxylic anions such as octoate and higher being preferred.
The desirability of providing new catalysts useful in producing polyurethane foams is exemplified by the following documents, which are incorporated herein in their entirety by reference thereto: U.S. Pat. No. 5,286,758 teaches the use of potassium formate dissolved in water. In this prior art, the water that is used to dissolve the potassium formate is the blowing agent. The foams produced according to this prior art are generally very friable. U.S. Pat. No. 5,162,385 teaches the use of potassium acetate in a solution of ethylene glycol. In this prior art method, the blowing agent is a carboxylic acid. European Patent Application 656382 teaches the use of a hydroxyalkyl quaternary ammonium trimerization catalyst, a carboxylic acid and a second trimerization catalyst.
It would be desirable to be able to use formic acid because the specific reaction rate for formation of isocyanurate varies inversely with the molecular weight of the organic acid. Also, it is known in the art that anions of lower carboxylic acids are more ionic in character than higher carboxylic acids, and it is readily observable that as the ionic character of the anion increases, the time to final cure of the polyurethane or polyisocyanurate formed in its presence is seen to be delayed in direct proportion to the ionic character of the ionic character of the anion. However, the only method of delivery heretofore has been a system which includes substantial amounts of water to render the alkali metal carboxylate soluble and provide it in a homogeneous state to a component or the components from which the polyurethane is derived. Unfortunately, as is well-known to those in the polymeric foam art, water reacts rapidly with isocyanates, especially in the presence of catalysts to form cyclic carbamic acids which decompose to primary amines with the evolution of carbon dioxide. The primary amine thus formed rapidly and deleteriously consumes substantial amounts of the isocyanate present with the resultant formation of highly crystalline urea(s). Small amounts of water are also capable of reacting with isocyanate, resulting in the rapid consumption of the isocyanate due to the low equivalent weight of water. Polyurethane foams produced in the presence of appreciable amounts of water are accordingly much more friable than foams produced in the absence of water, and the insulation value of foams produced without water are much improved over foams containing or formed in the presence of appreciable amounts of water. Therefore, it is desired that water be limited in the mixture when polyurethane foams are produced.
Accordingly, if a water-free composition and means were found which would provide for the introduction of essentially anhydrous catalysts which heretofore could only be introduced by having appreciable quantities of water present along with the catalysts, such would be a significant advance in the art which would open the doors to the use of a myriad of potential catalyst materials, thus providing the chemist with the ability to create new foams having previously unobserved properties. The present invention provides such compositions and means.